1. Field of the Invention
This invention relates to a developing apparatus used with, for example, an electronic copying apparatus.
2. Description of the Related Art
With an electronic copying apparatus, an original image is formed on a sensitive drum in the form of a static latent image. The latent image is made visible when applied with a developer. When a visible image formed on the photosensitive drum is transcribed on a paper sheet, the original is fully copied. The developer is formed of a toner acting as a coloring material with magnetic particles. This developer is magnetically transported to the photosensitive drum from a closely set developing vessel to be deposited in a latent image formed on the photosensitive drum. For the transport of the developer, a developing roller unit is received in the developing vessel. The developing roller comprises a cylindrical nonmagnetic sleeve and a plurality of magnets held in the sleeve. The developer is attracted to the sleeve by the magnetic force by the magnets. Then, the developer is transported by the rotation of the sleeve over its surface to the photosensitive drum. The toner is deposited on the latent image. The latent image is thus developed. In this connection, a multiroller type developing apparatus is known which comprises a plurality of developing rollers, received in a developing vessel, for the object of ensuring the efficient transportation/deposition of a single color developer or ensuring the transportation/deposition of a multicolor developer for color copying. However, this developing apparatus is accompanied with the drawbacks that if the adjacent rollers are narrowly spaced from each other, a magnetic flux is generated between the mutually-facing magnets of the adjacent developing rollers. In this case, a magnetic field acting in the normal direction of the sleeve circumference is more intensified than a magnetic field acting in the circumferential direction of the sleeve, thereby obstructing the transportation of the developer. Therefore, a distance between the respective developing rollers has to be widened in order to prevent a magnetic field acting in the normal direction from being stronger than a magnetic field acting in the circumferential direction of the sleeve. This undesirably leads to the enlargement of a developing apparatus.